Postal services utilize specialized equipment to transport, scan, sort and process tens of millions of envelopes and other flat pieces of mail on a daily basis. These automated systems and machines necessarily utilize specialized equipment designed to transport, scan, process and sort envelopes and other flat pieces of mail. To insure reliable operation of these machines, mail pieces having physical properties incompatible with automated processing equipment must be separated from the mail stream at the earliest opportunity. In particular, mail pieces that are too stiff or rigid to be transported must be diverted from automated processing lines to avoid jamming the machines and/or being destroyed during processing.
U.S. Pat. No. 7,096,743 issued Aug. 29, 2006 to Vogel, discloses an device for measuring the flexural rigidity in the longitudinal direction of flat items of mail a conveying path. The apparatus includes a sensor for detecting the edges of the items of mail and signaling a control device when a mail item reaches a selected bearing point. A deflection apparatus moves into the conveying path under the control of the control device to bend the mail item. The magnitude of the deflection of the mail item and the magnitude of the deflection force are measured to determine the flexural rigidity of the mail item.
Reisig, et al., U.S. Pat. No. 6,032,517, issued Mar. 7, 2000, discloses an arrangement for measuring the rigidity of flat items by means of elastic conveying belts that extend through a curved section of a conveying path. A rigidity sensor is provided for measuring the deflection of the conveying belts caused by the item passing through the curved section, and a thickness sensor is used to determine the thickness of the item. An evaluation device is provided for determining the rigidity of an item passing through from the values obtained by the thickness and rigidity sensors.
Redford U.S. Patent Application 20040245158, Dec. 9, 2004, describes a method and apparatus for stiffness and thickness detection in mail sorting systems by conveying a singulated stream of flat mail pieces one at a time though a test curve upstream from the sharpest curve of the mail processing machine, the test curve including an angled section at which each mail piece tends to bend, determining the thickness of each mail piece, determining the stiffness of each mail piece by measuring deflection of one of the belts of the test curve as an end portion of the mail piece is passing through the angled section, which deflection is in excess of deflection caused by the thickness of the mail piece as it passes between the belts, and diverting a mail piece out of the mail processing machine before it reaches the sharpest curve of the mail processing machine if predetermined stiffness and thickness criteria are exceeded by the thickness and stiffness of the mail piece. The angled section defines an angle less severe than the sharpest curve, whereby a mail piece that would likely jam the mail processing machine at the sharpest curve can pass through the test curve without jamming.
The foregoing devices require bending the mail pieces by transporting the mail pieces through a curved path. This in turn requires moving parts such as conveyors and rollers as well as space in which to install the devices. Elimination of these parts would simplify and reduce the size or length of the processing line. Ideally, a stiffness detector for use in an high speed automated mail processing line will process the mail without damaging individual mail pieces, have a small footprint, a minimum number of moving parts and will be capable of meeting the throughput requires of the line.